Non-regenerative hydromechanical transmission

ABSTRACT

An input means and an output means are connected together by a plurality of gear trains which are intermediately connected to each other by a first planet gear set of a planetary gear arrangement. The planetary gear arrangement also has a second planetary gear set intermeshed with the first set. The gear trains are of overlapping speed ratios and are successively connected to drive the output means through a pre-selected speed range, with means being provided for disconnecting each driving train from the output means after the following train has been connected to it. In a preferred form, the planetary gear set has a pair of alternately used output gears, both meshing with the first set of planet gears, one output gear being a sun gear, the other being a ring gear. A novel system employs each output gear, at times, in a reaction system incorporating a reaction gear meshed with the second planetary gear set. A first hydraulic unit is in driving engagement with that reaction gear and a second hydraulic unit is hydraulically connected to the first hydraulic unit, with one of the hydraulic units serving as a pump while the other one serves as a motor and vice versa. Means are provided for alternately connecting and disconnecting the output gears to the second hydraulic unit, for use in the reaction system.

United States Patent [1 1 Orshansky, Jr.

[ 51 Jan. 9, 1973 [54] NON-REGENERATIVE HYDROMECHANICAL TRANSMISSION [75] Inventor: Elias Orshansky, Jr., San Francisco,

Calif.

[73] Assignee: URS Systems Corporation, San

Mateo, Calif.

[22] Filed: Feb. 16, 1971 [211 Appl. No.: 115,596

3,306,129 2/1967 De Lalio ...74/687 3,383,953 5/1968 Christenson....74/687 X 3,580,107 5/1971 Orshansky, Jr ..74/687 PrimaryExaminer-William L. Freeh Assistant ExaminerThomas C. PerryAttorney-Owen, Wickersham & Erickson 57 ABSTRACT An input means and anoutput means are connected together by a plurality of gear trains whichare intermediately connected to each other by a first planet gear set ofa planetary gear arrangement. The planetary gear arrangement also has asecond planetary gear set intermeshed with the first set. The geartrains are of overlapping speed ratios and are successively connected todrive the output means through a preselected speed range, with meansbeing provided for disconnecting each driving train from the outputmeans after the following train has been connected to it. In apreferred" form, the planetary gear set has a pair of alternately usedoutput gears, both meshing with the first set of planet gears, oneoutput gear being a sun gear, the other being a ring gear. A novelsystem employs each output gear, at times, in a reaction systemincorporating a reaction gear meshed with the second planetary gear set.A first hydraulic unit is in driving engagement with that reaction gearand a second hydraulic unit is hydraulically connected to the firsthydraulic unit, with one of the hydraulic units serving as a pump whilethe other one serves as a motor and vice versa. Means are provided foralternately connecting and disconnecting the output gears to the secondhydraulic unit, for use in the reaction system.

20 Claims, 12 Drawing Figures PATENTEDJAH 9 I973 SHEET 1 OF 8PATENTEDJAH 9 I975 SHEET 2 [IF 8 INVENTOR. ELIAS ORSHANSKY JR.

BY 0W4 Q ATTORNEYS PATENTEDJAH ems 3.709.061

SHEET 3 BF 8 lV/A INVENTOR. I ELIAS ORSHANSKY,. JR.

Y 003%, I ZZMAM ATTORNEYS PATENTED JAN 9 I973 SHEET 8 OF 8 000? X ENEQmwnm ,SnFDO m L WY, (1% EK Q0 W M IN 4 M J w or 0 M w M G m E S v M V N3 3 o W 3 N N Ill" V I N w E m 9 m? @E AT "I 3 H N FYQ NON-REGENERATIVEHYDROMECHANICAL TRANSMISSION BACKGROUND OF THE INVENTIOH This inventionrelates to a non-regenerative hydromechanical transmission. A pair ofhydraulic units is employed in connection with a planetary geararrangement. This transmission is especially useful in trucks and otherautomotive vehicles.

A purpose of this invention is to provide a commercially producibletransmission which enables an improved method of utilizing vehicleengine power. This improved method makes it possible for the engine tooperate within a narrow speed range that has been optimized for minimumemissions, maximum fuel economy, and maximum power, regardless ofvehicle operating conditions.

Conventional torque converter and manual transmissions have imposed manycompromises upon the engine system, due to the requirement of providingadequate performance over a wide range of torques and speeds. Thepractice of most vehicle manufacturers of offering a selection ofoptional axle ratios for the vehicle purchaser is but one of manyattempts to reduce the compromise for any given application.

With an infinitely variable transmission, an engine can always beoperated in a speed range where it is capable of producing rated power;hence, vehicle performance in any given application can be maintained oreven improved while utilizing a substantially smaller engine. Infinitelyvariable transmissions of the pure hydrostatic type are limited toapplications where significant power losses can be tolerated in returnfor the benefits of improved transmission ratio control. Hydromechanicaltransmissions offer the control benefits of a hydrostatic transmissionbut by virtue of the fact that only a portion of the engine power istransmitted by the hydraulic units, they remove the performance barrierof excessive power losses. The extent to which any hydromechanicaltransmission can accomplish this end is strictly a function of thepercentage of power which must be transmitted hydraulically.

The invention provides for minimum hydraulic power transmission whileavoiding the pitfalls of excessive complexity, speeds, or loads in thegear trains. Maximum reliability and minimum cost can be obtained, byutilizing standard commercial hydraulic units which are operated totallywithin their long-life rated conditions of speed and power. In additionthe clutches can be of the low-cost types presently employed in highproduction automobile torque-converter transmissions. A smaller numberof elements can be utilized, however, for a comparable power rating,than in a torque converter transmission, due to the fact that at allshift points the clutch elements are virtually synchronous. The numberof elements is therefore a function not of their thermal capacity but oftheir steady-state torque capacity.

By applying the transmission of this invention to a piston engine,exhaust emissions can be reduced, and the specific fuel consumption canbe improved by programming the engine to operate within its optimumrange under all road conditions without regard to transmission torqueoutput. Both nitrogen oxide emissions and hydrocarbon emissions can beminimized, by optimizing the engine combustion process for operation ina specific narrow range. In addition, the invention enables the use of asmaller engine for any application, as the transmission will allow fullengine power to be developed at any vehicle speed except for the lowerspeeds where the vehicle is traction limited.

These same considerations also apply to a rotary combustion chamberengine, and there the benefits in reduction of hydrocarbon emissions areof much greater magnitude, due to the high rate of change in emissioncharacteristics for a rotary combustion chamber engine with respect toengine speed.

Benefits are also derived from the application of this type oftransmission to a gas turbine. The major drawback in producing suchturbines today is their cost of manufacture, and this cost is, to alarge degree, a function of the complexity necessitated by the design ofa turbine for use under the varying torque and speed requirements of aroad vehicle. The single-shaft type of turbine is not only moreeconomical to manufacture than the two-shaft design normally proposedfor vehicle application, but it is also more efficient if operatedwithin the band of its maximum efficiency. With the hydromechanicaltransmission of this invention, a turbine can be programmed to operateonly under those conditions during which it is most efficient.

The transmission of this invention is applicable to many fields,including passenger cars, highway trucks, and off-the-highway trucks,agricultural equipment, construction equipment, military vehicles, andindustrial drives.

In a prior invention of mine I provided a combination in which two setsof planet gears mounted on the same carrier meshed with each other. Thisinvention also employs that combination. However, in that priorinvention each set of planet gears meshed with a separate output member,typically two separate ring gears. In the present invention both of theoutput members mesh with the same set of planet gears. Also, in theformer invention, there were gear trains between the planetaryarrangement and the final output member, but in the present inventionthere are no gear trains between the planetary output members and thefinal output shaft; there are only clutches between them. This providesan important advantage, in that the driving torque is transmitted by theseveral planet meshes rather than by a single mesh at gears beyond theplanetary arrangement. Therefore, quite heavy loads can be applied tolighter gears.

A significance of the avoidance of overloading the single teeth of gearslies in the fact that torque developed in transmissions is high, andwhere there are any gear-ratio sets beyond the planetary assembly, thetooth loading of these gear sets becomes extremely high. By providing astructure in which the transmission has no output shifts beyond oroutside of the planetary assembly, this difficulty is minimized. In thisinvention, the output shifts are directly from the planetary membersto'the final output, and they are accomplished by means of clutches.Hence, no gear-tooth loads are involved there, and the only gear-toothloads which are encountered are those within the planetary gearassembly, where they are divided, since several planet gears are meshedwith the output gear, instead of just one pair of gears being meshedwith each other.

Another interesting distinction is that the planetary gear arrangementand the final output shaft are co-axial. A further difference is thatthe second set of intermeshing planet gears meshes only with the firstset and with a reaction gear.

A very important feature of the invention is the elimination ofregenerative horsepower. In the present invention, the hydraulichorsepower is handled by the hydraulic system either as additive withinthe planetary gear arrangement or as output coupled, where the hydraulicsystem adds power directly to the output. Thus, power can be handledover a wide range without regenerative power within the planetaryassembly. This makes it possible to use small hydraulic units and asmall number of gears and clutches. The invention is thereforecharacterized by great simplicity so far as the number of gears,clutches, and shafts are concerned and in relatively small size so faras the hydraulic units are concerned-and therefore in so far as theentire unit is concerned.

One of the reasons for the simplicity of the invention is that avariable speed planetary arrangement is used in place of what wouldotherwise have to be final steps of gearing.

The invention is significant in its great reduction of cornerhorsepower. Corner horsepower" is a term applied to the maximumhorsepower that the unit would be capable of, if it ran at a combinationof both its'maximum torque and its maximum speed, appliedsimultaneously. While this condition never actually arises, itssignificance is that it is the condition that governs the size of thehydraulic units. By holding corner horsepower down, the size of thehydraulic units is reduced.

This is a relatively wide ratio transmission, and thus is particularlysuited for use in trucks and other vehicles where a combination of highhorsepower and wide reduction ratio exists. In order to accomplish awide reduction efficiently, it is necessary to reduce the amount ofhydraulic horsepower being transmitted, and, in order to be able tobuild a commercially feasible unit, it is necessary to reduce the amountof corner horsepower and the size of the hydraulic unit, as describedabove. Moreover, as already stated, in accomplishing its highefficiency, this invention eliminates regenerative horsepower.

BRIEF SUMMARY OF THE INVENTION The input shaft transmits power,preferably through an intermediate gear, to a planetary input membersuch as a planet carrier. This carrier carries two sets of planet gearswhich are meshed with each other. Each of the two sets of planet gearsmeshes with a different sun gear, and the separate shafts on which thesun gears are mounted are co-axial with each other and with the finaloutput shaft. One set of the planet gears is meshed with, not only oneof the sun gears, but also with a ring gear and it is through thissingle set of planet gears that both of the two alternative outputs areobtained. One output is thus provided by the ring gear, which isclutchable directly to the final output shaft, and the other output isprovided by the sun gear meshed to the same planets as is the ring gear,and that sun gear is connected by clutching means directly to the finaloutput shaft.

The second set of planet gears engages the second sun gear on a shaftthat supports another gear which is meshed with a gear on an additionalshaft, which usually serves as a reaction shaft, but serves for outputpurposes during starting and reverse conditions. This reaction shaftdrives, or is driven by, one of two hydraulic units. The other hydraulicunit has its own auxiliary shaft, and the two units are hydraulicallyconnected togethenThe auxiliary shaft mounts a pair of auxiliary gears,one of which meshes with a gear on the shaft carrying the output sungear, and the other meshes with a gear rigidly mounted on the samestructure as the output ring gear. These two auxiliary gears are eachseparately clutchable to the auxiliary shaft. Through these, the outputgear which is not being used for output, is used in the reaction systemat some times and is used to add hydraulic power directly to the outputwithout transmitting that hydraulic power through the gear teeth of theplanetary gearing.

The reaction shaft also supports a gear that is used during starting andreverse operations, to drive a gear which is clutchable to the finaloutput shaft.

In order to simplify the description of operation of the invention andto set forth a complete description, so that other objects andadvantages of the invention will become apparent, the following detaileddescription ofa preferred embodiment is given.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a diagrammatic view generally in elevation and in section of atransmission embodying the principles of the invention. Certain gearsare shown not touching, though they are actually in mesh, with brokenlines indicating their touching, the true position of these gears beingshown in other figures.

FIG. 2 is a view in section taken along the line 22 in FIG. 1.

FIG. 3 is a view in section taken along the line 33 in FIG. 1.

FIG. 4 is a view in section taken along the line 4-4 in FIG. 1. i

FIG. 5 is a view in section taken along the line 5-5 in FIG. 1.

FIG. 6 is a view in section taken along the line 66 in FIG. 1.

FIG. 7 is a fragmentary view of a portion of a transmission generallysimilar to that of FIG. 1 but with a modification therein.

FIG. 8 is a graph of the transmission and hydraulic I unit torquesproduced by the form of the invention plotted against the output speedin increments of 1,000 RPM.

FIG. 11 is a graph of the hydraulic pressure for the transmission ofFIGS. 1 through 6, with the hydraulic pressure in pounds per square inchin increments of 1,000 plotted against the output speed in increments of1,000 RPM.

FIG. 12 is a graph of the hydraulic unit displacement for thetransmission of FIGS. 1 through 6, with the displacement in cubic inchesplotted against the output speed in increments of 1,000 RPM.

DESCRIPTION OF A PREFERRED EMBODIMENT An input shaft 20 acts throughgears 21 and 22 to drive a planet carrier 23 having shafts 24, andforming part of a planetary gear assembly 25. Thus, in this transmissionthe planet carrier 24 serves as the input member of the planetary gearassembly 25. The planet carrier 24 carries two intermeshing sets ofplanet gears 26 and 27. In FIG. 1, only one of each of the gears 26 and27 is shown, with the others being shown in FIGS. 4 and 5.

The planet gears 26 all mesh with a ring gear 30 and an output sun gear31, which are the two output gears of the planetary gear assembly andare used alternately. As will be seen later, during part of the timewhile the gear 30 is being used as an output gear, the gear 31 is beingused for reaction, and vice versa. The ring gear 30 forms part of anassembly 32, providing a gear 33 and a clutching portion 34. Theclutching portion 34 is engageable with a clutching portion 35 that isrigidly secured to a final output shaft 36. It should be noted that thering gear 30 and its assembly 32 are co-axial with the final outputshaft 36, as are the planetary gear assembly 25 itself and the outputsun gear 31.

The output sun gear 31 is mounted rigidly on a shaft 37 which hasclutching elements 38 that are engageable by clutching elements 39 whichare directly connected to the final output shaft 36.

From what has been said already it will be evident that the planetarygear assembly 25 provides three gears 26 meshing with both of the outputgears 30 and 31, so that power flow is minimized at these meshes. Beyondthese points there are no gears between these output gears 30 and 31 andthe final output shaft 36 only the clutches 34, 35 and 38, 39 by whichthe output gears 30 and 31 are alternately clutched to or unclutchedfrom the final output shaft 36. Generally, only one output at a timewill be clutched to the shaft 36 except during the actual shifting fromone to the other; then, one of the clutches is already engaged, and thesecond one is engaged before the first one is disengaged.

The shaft 37 which carries the output sun gear 31 also carries a gear 40which meshes (see FIG. 2) with a gear 41 that is mounted on, andclutchable to an auxiliary shaft 42 by a suitable clutch 43. Theauxiliary shaft 42 also carries a clutch 44 by which a gear 49 can beclutched to the shaft 42. The gear 49 engages the gear 33, which isrigidly attached to the ring gear 30. From this it will be apparent thatthe auxiliary shaft 42 is clutchable alternately to gears which aredriven directly by either of the two output gears 30 and 31, and againthis clutching is done at different times with an overlap between them.

The auxiliary shaft 42 is in driving relation to a hydraulic A unit 45,which is connected by conduits 46 and 47 to a hydraulic B unit 48. Thehydraulic B unit 48 is in driving relation with a shaft 50 which usuallyoperates as a reaction shaft and rigidly carries a gear 51 that ismeshed to a gear 52. The gear 52 is rigidly connected by a shaft 53 to asecond sun gear 54 that meshes with the second set of planet gears 27.Note that the second set of planet gears 27 meshes only with the secondsun gear 54 and with the other planet gears 26. The second sun gear 54operates principally as a reaction gear, as will be seen.

The shaft 50 carries a gear 56, and the gear 56 may be connected throughan idler gear 57 on a shaft 58 to a gear 59 that is clutchable to thefinal output shaft 36, by a clutch 55.

Auxiliary pumps 60 may be driven by the input shaft 30 forsupercharging, lubricating, etc., the transmission. Due to high speed ofrotation, the case of the transmission (not shown) is preferablyoperated with a dry sump; so one of the pumps 60 scavenges the case,drives the oil through an oil cooler, and returns it to an oilreservoir. Another pump of the pumps 60 picks oil up from the reservoirand puts it through a filter and through a check valve into whicheverhydraulic line (e.g., 46 or 47) is the low pressure line. This makes upleakage within the hydraulic system, and feeds oil through orifices forlubrication of gears and bearings. A relief valve maintains the outletof this pump at about PSI. A third pump of the pumps 60 picks up oilfrom the reservoir and supplies pressure for clutch and hydraulic unitactuation. A relief valve for this circuit may be set at approximately400 PSI. It is possible to combine some or all of the functions of thesepumps, so that two or even one pump may be used to serve all the abovefunctions.

The clutches are all schematically shown as multiple plate frictionclutches, but they may be dog clutches or other types of clutches, dueto the almost perfect synchronization at all the shift points.

The two hydraulic units 45 and 48 are both variable units and areconnected together so that when one operates as a pump, the otheroperates asa motor and vice versa. Thus, in the starting and reverseranges and in speed Range 11 the hydraulic A unit 45 operates as a pump,and its stroke gradually decreases until it reaches zero at a shiftpoint and then in speed Ranges I and III increases in the oppositedirection, the A unit 45 then operating as a motor. Conversely, the Bunit 48 operates as a motor in starting and reverse and in speed Range11; its speed gradually slows to zero at a shift point and then it turnsin the opposite direction in speedRanges I and 111, operating as a pump.At the shifting points from Range l to Range 11 and from Range III toRange IV, the A unit 45 that has immediately prior to that point beenoperating as a motor becomes a pump, and the B unit 48 which has beenoperating as a pump again becomes a motor.

During starting and reverse, the clutches 55 and 44 are engaged. Thedirection of rotation of the output shaft 36 is determined by thestroking mechanism of the hydraulic A unit 45. At the shift from thestarting range to Range 1, (see FIG. 9), the clutch 34, 35 is engagedand, immediately afterwards the clutch 55 is disengaged. In shiftinginto Range 11 (FIG. 9) the clutch 34, 35 remains engaged, the clutch 43is engaged, and then the clutch 44 is disengaged. In shifting from RangeII into Range III, the clutch 38, 39 is engaged and then the clutch 34,35 is disengaged, the clutch 43 remaining engaged. In shifting fromRange III to Range IV the clutch 38, 39 remains engaged, the clutch 44is engaged again, and the clutch 43 is then disengaged. Thus, theclutches 43 and 44 are overlapping and one is engaged before the otheris disengaged at the point where the change is made between them.Similarly the clutches 34, 35, and 38, 39 overlap at the point ofshifting when the speeds are synchronized.

Starting with the speed of the output shaft 36 at zero and a givenconstant speed on the input shaft 20, the starting range requires thatthe clutches 44 and 55 be engaged, as described. Consequently, the powergoes from the shaft through the gears 21 and 22 into the carrier 23. Inthis starting range and in reverse and at no other time, the reactionsun gear 54 is an output gear; it then delivers power to the gear 52 andthrough the gear 51 to the reaction shaft 50 and thence through the gear56 to the idler 57 and the output gear 59, which is then clutched to theoutput shaft 36 by the clutch 55. Thus the mechanical power flowproceeds from the gear 21 via the gear 22, the carrier 23, the planetgears 26, the planet gears 27, the sun gear 54, and the gears 52 and 51to the shaft 50 and from there via the gears 56, 57 and 59 to the outputshaft 36. The flow of power to drive the hydraulic A unit 45 also entersfrom the input shaft 20 by the same path to the carrier 23 and theplanet gears 26. From there this power goes to the ring gear 30 and fromthere through the gear 33 and the gear 49 to the auxiliary shaft 42. Thehydraulic A unit 45 then acts as a pump and delivers hydraulichorsepower to the B unit 48. The B unit 48 then adds its power to thereaction shaft 50, and therefore to the output shaft 36. This startingrange extends from zero speed to the point where the input reaches fullhorsepower, and during this range the output torque is constant.

As soon as the input reaches this constant horsepower level, Range I isentered. In order to enter this range the output clutch 34, 35 isengaged just prior to disengagement of the clutch 55. The clutch 44remains engaged. At this point the ring gear 30 becomes the output gear,and the sun gear 54 becomes the reaction gear. Consequently, the A unit45 becomes a motor, although it has been a pump throughout the startingrange, and the B unit 48 becomes a pump. The A unit 45 adds its torqueto the output shaft 36 via the gears 49 and 33, which lie beyond theplanetary gear assembly 25. This is a very important feature, for it iswhat makes the transmission non-regenerative. The power is divided bythe planetary gear assembly into a hydraulic path and a mechanical path,and then the hydraulic power is added to the output shaft 36 beyond theplanetary gear assembly 25.

Range I continues, as shown on the speed line in FIG. 9 and the strokeof the A unit 45 is reduced as the speed increases, as shown in FIG. 12.At the point where the stroke in FIG. 12 of the A unit 45 reaches zero,the B unit 48, which has been decreasing its speed as shown in FIG. 9,comes to a standstill. Throughout Range I, the B unit 48 has been inconstant displacement, and the A unit 45 has been decreasing its strokefrom the beginning of that range until its end where it reaches zerodisplacement. At that time the A unit 45 is therefore spinning withouttransmitting power, so that a no-power shift can be made, and at thispoint the shift is made from Range I to Range II by engaging the clutch43 and then disengaging the clutch 44. In this instance, the exactaccuracy of the overlap is not as important as in the change from theclutch 34, 35 to the clutch 38, 39 since the A unit 45 transmits nohorsepower and is spinning on zero stroke.

The hydraulic pressure remains constant throughout Range I, as shown inFIG. 11. This is an advantage of the non-regenerative system whichavoids a very high spike of pressure that would be encountered in aregenerativeoperation. This operation during Range I may be calledoutput coupled, because the hydraulic power is added directly to theoutput by the A unit 45, and the B unit 48 is acting as a pump with theA unit 45 acting as a motor.

After the shift from Range I to Range II, which engages the clutch 43and connects the A unit 45 to the gears 41 and 40, the sun gear 31begins to act as a reaction gear. The hydraulic A unit 45 begins to bestroked in the opposite direction, as shown in FIG. 12, so that whereaspreviously it was a motor now it begins to act as a pump and transmitshorsepower through the B unit 48, which now acts as a motor whilecontinuing to be connected to the gears 51 and 52 and therefore to thereaction sun gear 54. The drive continues to be transmitted mechanicallythroughthe output ring gear 30 and the clutch 34, 35 to the output shaft36. The B unit 48 rotates in such a direction as further to speed up theoutput gear 30. This also occurs without recirculating any hydraulichorsepower through the planetary gear assembly 25, and thus regenerativehorsepower in the transmission is again avoided.

While the speed of the output ring gear 30 is being increased throughoutRanges I and II, the speed of the sun output gear 31 has beendecreasing. Of course, this gear 31 has been disconnected from theoutput because the clutch 38, 39 is not engaged in Ranges I and II. Atthe end of Range II, the speeds of the gears 30 and 31 are substantiallyequal, and theyare also substantially equal to the speed of the carrier23. At this equal speed point, an output shift is made to shift thepower transmission from the gear 30 to the gear 31 by first engaging theclutch 38, 39 and then immediately thereafter disengaging the clutch 34,35. This is a loaded power shift and an overlap in the engagement anddisengagement of the clutches must exist in order to avoid interruptionof power flow.

As soon as this shift is accomplished, Range III is entered. Thefunctions of the hydraulic units are now reversed, and the hydraulic Aunit 45," while still connected to the sun gear 31 through the clutch 43is now also connected to the output shaft 30 through the clutch 38, 39.The A unit 45 now begins to act again as a motor, and the transmissionenters another output coupled mode of operation. This continuesthroughout Range III, with the hydraulic A unit 45 gradually ad dingless and less torque to the output by reducing its displacement to zero,while the hydraulic B unit 48 remains at constant displacement. As inRange I, the pressure is a constant in Range III.

At the end of Range III, a hydraulic unloaded shift is made into RangeIV, at the time when the hydraulic A unit 45 reaches zero stroke. Thenit is disconnected from the gear 31 by unclutching the clutch 43immediately after it has been connected to the ring gear 30 byenergizing the clutch 44. The unloaded shift means again that the timingproblem is not so critical as in the loaded shift. Once that shift ismade, the hydraulic units again go through the same mode of operationalready described in connection with Range ll; thus the A unit 45 isstroked past zero in the opposite direction and acts as a motor torotate the gear 30 in a direction that further speeds up the output gear31. Range IV continues, with the sun gear 31 serving as the output gearand the ring gear 30 serving as a second reaction gear, in addition tothe reaction gear 54.

The horsepowers and the relation of the hydraulic horsepower to thetotal horsepower are shown in FIG. 10.

FIG. 7 provides an improved reverse operation. The input shaft carries agear 61 meshed with a gear 62 that is around the auxiliary shaft 42 andis clutchable to it by a clutch 63. The system of FIGS. 1-6 relies onthe hydraulic power exceeding the mechanical power in reverse, acting inopposition to it and overcoming it. Consequently, it is inefficient inreverse and incapable of developing much speed. The system of FIG. 7eliminates mechanically transmitted power in reverse (since it wouldthen be in opposition to the direction of drive) and is therefore ableto use the hydraulic power unopposed. It is a hydrostatic reverse andcan attain whatever speed the hydraulic system is capable of attaining.

When the clutch 63 is engaged and at this time no other clutch isengaged except the clutch 55 the power flows directly from the enginethrough the shaft 20, gears 61 and 62, clutch 63, and shaft 42 to drivethe hydraulic A unit 45 as a pump and delivers power to the B unit 48,acting as a motor. The B unit 48 drives the output shaft 36 through theshaft 50 and the gears 56, 57, and 59. The planetary assembly 25performs no function at this time.

The system of FIG. 7 can also be used in the starting range by properselection of the sizes of hydraulic units 45 and 48 and of gear ratiosof the gears 61 and 62. It reduces the maximum pressure in starting.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

I claim:

1. A power transmission comprising input means, output means, and aplurality of gear trains intermediately connected to each other by afirst planet gear set of a planetary gear assembly having a secondplanet gear set intermeshed with said first set, said trains being ofoverlapping speed ratios for connecting said input and output means, andeach having an output gear, means for successively connecting saidoutput gear of each train to drive the output means through apreselected speed range, means for disconnecting each driving train fromthe output means after the following train has been connected thereto, areaction gear in mesh with said second planet gear set, a firsthydraulic unit in driving engagement with said reaction gear, a

second hydraulic unit hydraulically connected to said first hydraulicunit, one said hydraulic unit serving as a pump while the other oneserves as a motor, and vice versa, and means for alternately connectingand disconnecting each said output gear to said second hydraulic unit,to serve as a reaction gear under some conditions and under otherconditions to add torque to said output means from said hydraulic unitswithout the hydraulically transmitted power going through said planetaryassembly.

2. The power transmission of claim 1 having a gear clutchable to saidoutput means, a gear secured to a shaft in driving relation to saidfirst hydraulic unit, and a gear train connecting those two gears, foruse in a reverse range and in a starting range.

3. The power transmission of claim 1 having a gear associated with saidinput means and meshed to a gear that is associated with said secondhydraulic unit, and clutching means for establishing through these gearsa driving connection between said input means and said second hydraulicunit, for use in a purely hydrostatic start and reverse range.

4. The power transmission of claim 1 wherein said output means and saidplanetary gear arrangement are co-axial.

5. A power transmission comprising driving means,

a planetary gear train connected to said means and having first andsecond sets of planet gears and a common carrier, one set beingintermeshed with the other,

a pair of output gears each in mesh with said first set of planet gears,

a reaction gear in mesh with said second set of planet gears,

a first hydraulic unit in driving engagement with said reaction gear,

a second hydraulic unit hydraulically connected to said first hydraulicunit, one said hydraulic unit serving as a pump while the other oneserves as a motor, and vice versa,

an output shaft,

clutch means for directly connecting each said output gear to saidoutput shaft, and

means for alternately connecting and disconnecting each said output gearto said second hydraulic unit to function as a reaction gear in someinstances and in other instances to add power to said output shaftwithout sending that added power through the planetary gear train.

6. The power transmission of claim 5 having means for causing the ratioof maximum speed to minimum speed for both said output gears to be thesame.

7. The power transmission of claim 5 wherein no member of the planetarygear train, except the planet gears, can have a speed in excess of themaximum of the higher speed output gear.

8. The power transmission of claim 5 having an output shaft and meansfor clutching said output shaft directly to either said output gear,said planetary gear arrangement being co-axial with said output shaft.

9. The power transmission of claim 5 wherein said first hydraulic unithas a shaft in driving relation thereto, and a gear train and clutchingmeans for connecting that said shaft in direct driving relation to saidoutput shaft.

10. The power transmission of claim 9 having a gear train and clutchingmeans for connecting said input shaft to said second hydraulic unit.

11. A power transmission comprising input means,

output means,

a pair of gear trains for alternately connecting said input means withthe output means, the trains comprising transmission ranges of differentratios and including a planetary gear assembly with a first set ofplanet gears intermeshed with a second set of planet gears and a commoncarrier for both sets of planet gears driven by said input means, a pairof output gears both meshing with said first set of planet gears, theends of said ranges overlapping from one train to the next,

means for alternately connecting and disconnecting the gear trains tothe output means at said overlapping ends, whereby power is transmittedalternately from said gear trains through the transmission ranges togradually drive the output means through the speed ranges,

a reaction gear meshed with the second set of planet gears,

a first hydraulic unit in driving engagement with said reaction gear,

a second hydraulic unit hydraulically connected to said first hydraulicunit, one said hydraulic unit serving as a pump while the other oneserves as a motor, and vice versa, and

means for alternately connecting and disconnecting each said output gearto said second hydraulic unit.

12. The power transmission of claim 11 wherein said first hydraulic unithas a shaft in driving relation thereto and a gear train and clutchcombination for placing that said shaft in direct driving relation tosaid output means.

13. The power transmission of claim 11 wherein said planetary geararrangement and said output means are co-axial.

14. The power transmission of claim 11 wherein the ratio of maximumspeed to minimum speed is the same for both output gears.

15. A power transmission comprising an input shaft having an input gearsecured thereto,

an output shaft,

a planetary gear assembly having a single carrier, first and second setsof mutually intermeshing planet gears, a first sun gear meshed with saidfirst set, a ring gear meshed with said first set, and a second sun gearmeshed with said second set, said carrier having rigidly associatedtherewith a gear meshed with said input gear,

clutching means for directly clutching said ring gear to said outputshaft,

clutching means for directly clutching said first sun gear to saidoutput shaft,

a shaft for said second sun gear with an additional gear thereon,

a reaction shaft with a gear thereon meshed with said additional gear,

a first hydraulic unit in driving relation with said reaction shaft,

a second hydraulic unit hydraulically connected to said first hydraulicunit,

one said hydraulic unit serving as a pump while the other said hydraulicunit serves as a motor and vice versa,

an auxiliary shaft in driving relation to said second hydraulic unit,

a shaft connected to and supporting said first sun gear and havingthereon a driven gear,

a gear meshed with said driven gear and clutchable to said auxiliaryshaft,

a transmitting gear rigidly connected to said ring gear, and

a gear meshed with said transmitting gear and clutchable to saidauxiliary shaft.

16. The power transmission of claim 15 wherein both said sun gears andtheir shafts and said planetary assembly and said output shaft areco-axial.

17. The power transmission of claim 15 having a starting and reversegear secured to said reaction shaft,

a drive gear mounted around said output shaft,

a clutch for clutching said drive gear to said output shaft, and

intermediate gear means connecting said starting and reverse gear tosaid drive gear.

18. The power transmission of claim 17 having a gear secured to saidinput shaft,

a gear meshed to that gear, and

clutch means for clutching the last-named gear to said auxiliary shaft.

19. A method of operating a transmission of the type having a planetarygear assembly with a rotary input member, a rotary reaction member, anda pair of rotary output members, said transmission also having a pair offluid pump-motors hydraulically connected together, each able to serveas a pump at some times and as a motor at other times, one serving as apump when the other serves as a motor and vice versa, a first saidpump-motor being connected to said rotary reaction member, a secondpump-motor alternately connected by clutching and gear trains to each ofsaid rotary output members, a main output shaft, and clutch means fordirectly clutching said main output shaft to each said rotary outputmember, comprising the steps of:

l. continuously driving said rotary input member,

2. transmitting torque from said rotary input member to said main outputshaft through a first said rotary output member,

3. causing said first pump-motor to progress from its maximum speed tozero speed,

4. simultaneously causing said second pump-motor, to decrease itsdisplacement from maximum to zero stroke,

5. whereby said first rotary output member increases its speed and thespeed of the main output shaft while said second rotary output memberdecreases its speed,

6. shifting synchronously the drive to said second pump-motor from saidfirst rotary output member to said second rotary output member at anoverlapping ratio,

7. 'reversing the functional operation of said two pump-motors, so thatthe second pump-motor progresses from zero stroke to full stroke in theopposite direction from before the shifting step while the firstpump-motor increases from zero speed to pump-motors, and

10. continuing to increase the speed of said main output shaft byoperating the pump-motors again as in steps (3), (4), (5), (6) and (7).

20. The method of claim 19 characterized by a constant ratio between themaximum and minimum speeds of said main output shaft for both saidrotary output members.

1. A power transmission comprising input means, output means, and aplurality of gear trains intermediately connected to each other by afirst planet gear set of a planetary gear assembly having a secondplanet gear set intermeshed with said first set, said trains being ofoverlapping speed ratios for connecting said input and output means, andeach having an output gear, means for successively connecting saidoutput gear of each train to drive the output means through apreselected speed range, means for disconnecting each driving train fromthe output means after the following train has been connected thereto, areaction gear in mesh with said second planet gear set, a firsthydraulic unit in driving engagement with said reaction gear, a secondhydraulic unit hydraulically connecTed to said first hydraulic unit, onesaid hydraulic unit serving as a pump while the other one serves as amotor, and vice versa, and means for alternately connecting anddisconnecting each said output gear to said second hydraulic unit, toserve as a reaction gear under some conditions and under otherconditions to add torque to said output means from said hydraulic unitswithout the hydraulically transmitted power going through said planetaryassembly.
 2. The power transmission of claim 1 having a gear clutchableto said output means, a gear secured to a shaft in driving relation tosaid first hydraulic unit, and a gear train connecting those two gears,for use in a reverse range and in a starting range.
 2. transmittingtorque from said rotary input member to said main output shaft through afirst said rotary output member,
 3. causing said first pump-motor toprogress from its maximum speed to zero speed,
 3. The power transmissionof claim 1 having a gear associated with said input means and meshed toa gear that is associated with said second hydraulic unit, and clutchingmeans for establishing through these gears a driving connection betweensaid input means and said second hydraulic unit, for use in a purelyhydrostatic start and reverse range.
 4. The power transmission of claim1 wherein said output means and said planetary gear arrangement areco-axial.
 4. simultaneously causing said second Pump-motor, to decreaseits displacement from maximum to zero stroke,
 5. A power transmissioncomprising driving means, a planetary gear train connected to said meansand having first and second sets of planet gears and a common carrier,one set being intermeshed with the other, a pair of output gears each inmesh with said first set of planet gears, a reaction gear in mesh withsaid second set of planet gears, a first hydraulic unit in drivingengagement with said reaction gear, a second hydraulic unithydraulically connected to said first hydraulic unit, one said hydraulicunit serving as a pump while the other one serves as a motor, and viceversa, an output shaft, clutch means for directly connecting each saidoutput gear to said output shaft, and means for alternately connectingand disconnecting each said output gear to said second hydraulic unit tofunction as a reaction gear in some instances and in other instances toadd power to said output shaft without sending that added power throughthe planetary gear train.
 5. whereby said first rotary output memberincreases its speed and the speed of the main output shaft while saidsecond rotary output member decreases its speed,
 6. shiftingsynchronously the drive to said second pump-motor from said first rotaryoutput member to said second rotary output member at an overlappingratio,
 6. The power transmission of claim 5 having means for causing theratio of maximum speed to minimum speed for both said output gears to bethe same.
 7. The power transmission of claim 5 wherein no member of theplanetary gear train, except the planet gears, can have a speed inexcess of the maximum of the higher speed output gear.
 7. reversing thefunctional operation of said two pump-motors, so that the secondpump-motor progresses from zero stroke to full stroke in the oppositedirection from before the shifting step while the first pump-motorincreases from zero speed to maximum speed in the opposite direction ofrotation and so that said second rotary output member continues todecrease its speed while the speed of said first rotary output membercontinues to increase until said first and second rotary output membersare at the same speed,
 8. shifting synchronously the drive to said mainoutput shaft from said first rotary member to said second rotary member,8. The power transmission of claim 5 having an output shaft and meansfor clutching said output shaft directly to either said output gear,said planetary gear arrangement being co-axial with said output shaft.9. The power transmission of claim 5 wherein said first hydraulic unithas a shaft in driving relation thereto, and a gear train and clutchingmeans for connecting that said shaft in direct driving relation to saidoutput shaft.
 9. again reversing the functional operation of saidpump-motors, and
 10. continuing to increase the speed of said mainoutput shaft by operating the pump-motors again as in steps (3), (4),(5), (6) and (7).
 10. The power transmission of claim 9 having a geartrain and clutching means for connecting said input shaft to said secondhydraulic unit.
 11. A power transmission comprising input means, outputmeans, a pair of gear trains for alternately connecting said input meanswith the output means, the trains comprising transmission ranges ofdifferent ratios and including a planetary gear assembly with a firstset of planet gears intermeshed with a second set of planet gears and acommon carrier for both sets of planet gears driven by said input means,a pair of output gears both meshing with said first set of planet gears,the ends of said ranges overlapping from one train to the next, meansfor alternately connecting and disconnecting the gear trains to theoutput means at said overlapping ends, whereby power is transmittedalternately from said gear trains through the transmission ranges togradually drive the output means through the speed ranges, a reactiongear meshed with the second set of planet gears, a firSt hydraulic unitin driving engagement with said reaction gear, a second hydraulic unithydraulically connected to said first hydraulic unit, one said hydraulicunit serving as a pump while the other one serves as a motor, and viceversa, and means for alternately connecting and disconnecting each saidoutput gear to said second hydraulic unit.
 12. The power transmission ofclaim 11 wherein said first hydraulic unit has a shaft in drivingrelation thereto and a gear train and clutch combination for placingthat said shaft in direct driving relation to said output means.
 13. Thepower transmission of claim 11 wherein said planetary gear arrangementand said output means are co-axial.
 14. The power transmission of claim11 wherein the ratio of maximum speed to minimum speed is the same forboth output gears.
 15. A power transmission comprising an input shafthaving an input gear secured thereto, an output shaft, a planetary gearassembly having a single carrier, first and second sets of mutuallyintermeshing planet gears, a first sun gear meshed with said first set,a ring gear meshed with said first set, and a second sun gear meshedwith said second set, said carrier having rigidly associated therewith agear meshed with said input gear, clutching means for directly clutchingsaid ring gear to said output shaft, clutching means for directlyclutching said first sun gear to said output shaft, a shaft for saidsecond sun gear with an additional gear thereon, a reaction shaft with agear thereon meshed with said additional gear, a first hydraulic unit indriving relation with said reaction shaft, a second hydraulic unithydraulically connected to said first hydraulic unit, one said hydraulicunit serving as a pump while the other said hydraulic unit serves as amotor and vice versa, an auxiliary shaft in driving relation to saidsecond hydraulic unit, a shaft connected to and supporting said firstsun gear and having thereon a driven gear, a gear meshed with saiddriven gear and clutchable to said auxiliary shaft, a transmitting gearrigidly connected to said ring gear, and a gear meshed with saidtransmitting gear and clutchable to said auxiliary shaft.
 16. The powertransmission of claim 15 wherein both said sun gears and their shaftsand said planetary assembly and said output shaft are co-axial.
 17. Thepower transmission of claim 15 having a starting and reverse gearsecured to said reaction shaft, a drive gear mounted around said outputshaft, a clutch for clutching said drive gear to said output shaft, andintermediate gear means connecting said starting and reverse gear tosaid drive gear.
 18. The power transmission of claim 17 having a gearsecured to said input shaft, a gear meshed to that gear, and clutchmeans for clutching the last-named gear to said auxiliary shaft.
 19. Amethod of operating a transmission of the type having a planetary gearassembly with a rotary input member, a rotary reaction member, and apair of rotary output members, said transmission also having a pair offluid pump-motors hydraulically connected together, each able to serveas a pump at some times and as a motor at other times, one serving as apump when the other serves as a motor and vice versa, a first saidpump-motor being connected to said rotary reaction member, a secondpump-motor alternately connected by clutching and gear trains to each ofsaid rotary output members, a main output shaft, and clutch means fordirectly clutching said main output shaft to each said rotary outputmember, comprising the steps of:
 20. The method of claim 19characterized by a constant ratio between the maximum and minimum speedsof said main output shaft for both said rotary output members.